Effects of annealing with CO and CO2 molecules on oxygen vacancy defect density in amorphous SiO2 formed by thermal oxidation of SiC

Kenta Chokawa,Masaaki Araidai,Kenji Shiraishi

doi:10.1063/1.5041794

Abstract

SiO2 formed by the thermal oxidation of SiC has numerous defects, and the stoichiometry of the SiO2 near the SiC/SiO2 interface differs from that of SiO2 near the Si/SiO2 interface. We assume that, during the oxidation of SiC, CO and CO2 molecules are released, and that these molecules interact with the SiO2 and form defects. Considering the Gibbs free energy of these molecules, we found that CO molecules reduce part of the amorphous SiO2 at high temperatures, resulting in the formation of oxygen vacancy defects concomitant with the formation of CO2 molecules. In particular, when the partial pressure of the CO molecules is higher than that of the CO2 molecules, the number of oxygen vacancy defects increases. This means that post-oxidation annealing with CO molecules induces defects and degrades the breakdown field of SiO2. On the other hand, when the partial pressure of the CO2 molecules is larger than that of the CO molecules, reduction by the CO molecules does not occur, and the CO2 molecules can oxidize oxygen vacancy defects in SiO2. This means that post-oxidation annealing with CO2 molecules enables recovery of the oxygen vacancy defects and improves the breakdown field and flatband shift of SiO2 gate dielectrics. Accordingly, it is possible to reduce the formation of oxygen vacancies in amorphous SiO2 by performing post-oxidation annealing in a CO2 gas ambient.

Highlights

The potential utility of SiC metal-oxide-semiconductor field effect transistors (MOSFETs) for the realization of highperformance power devices capable of operation at higher temperatures and a higher power density, with lower energy consumption than Si MOSFETs, has been explored.[1,2] SiC has a larger bandgap, higher thermal conductivity, and higher breakdown field than Si, exhibiting greater potential for realizing such high-performance power devices
Considering the Gibbs free energy of these molecules, we found that CO molecules reduce part of the amorphous SiO2 at high temperatures, resulting in the formation of oxygen vacancy defects concomitant with the formation of CO2 molecules
On the other hand, when the partial pressure of the CO2 molecules is larger than that of the CO molecules, reduction by the CO molecules does not occur, and the CO2 molecules can oxidize oxygen vacancy defects in SiO2. This means that post-oxidation annealing with CO2 molecules enables recovery of the oxygen vacancy defects and improves the breakdown field and flatband shift of SiO2 gate dielectrics

Summary

INTRODUCTION

The potential utility of SiC metal-oxide-semiconductor field effect transistors (MOSFETs) for the realization of highperformance power devices capable of operation at higher temperatures and a higher power density, with lower energy consumption than Si MOSFETs, has been explored.[1,2] SiC has a larger bandgap, higher thermal conductivity, and higher breakdown field than Si, exhibiting greater potential for realizing such high-performance power devices. VO defects have an Si–Si dimer structure and form occupied levels near the valence band maximum of SiO2.18 In addition, when the Si–Si dimer structure traps electrons or holes, structural changes occur, resulting in the formation of Si dangling bonds.[19,20]. These dangling bond states appear in the midgap of SiO2 and are the causes of stress-induced leakage current.[21]. The formation of SiC nanocrystals occurs when the Si substrate is thermally oxidized by the CO molecules, resulting in the formation of SiO2,23 and it has been reported that the thermal oxidation of a Si substrate induces the emission of Si atoms from the interface.[12]. In this study, we investigated the formation of VO defects caused by the reduction of the SiO2 by CO molecules

CALCULATION DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS